Many cameras and other film handling devices now use thrust cartridges having active light locks, sometimes called "light valves", rather than the plush light traps used in conventional cartridges. Advanced Photo System.TM. (APS.TM.) cameras and devices use this type of cartridge. Such film cartridges include a coiled filmstrip within an canister having a longitudinally extending opening for exit of the filmstrip from the cartridge. A filmstrip is wound around a cartridge spool that is rotatably positioned within the canister. The active light lock is a hatch that is mounted adjacent the cartridge opening and is movable between an open state, in which the filmstrip can be moved into and out of the cartridge; and a closed state, in which the cartridge is light-tightly sealed.
Unlike conventional film cartridges (such as "35 mm", that is, Type 135 film cartridges) thrust film cartridges have no film leader extending out of the cartridge to indicate that the film is unexposed. Consequently, some other means is required to indicate whether unexposed frames exist on the film contained within the film cartridge. One such means, used in APS cartridges, is one or more visual indicator visible from the exterior of a film cartridge. One type of visible indicator is in the form of icons. The film spool can be rotated to align the visual indicator with icons on the exterior of the film cartridge, for example, specially formed icon openings to designate the film as being: unexposed, partially exposed, fully exposed, or processed. Another visible indicator is a radial bar code disposed on a data disk positioned at an axial end of the film cartridge. The data disk is rotatable with the rotation of the film spool contained within the film cartridge during film advancement and rewind. The radial bar code is typically read by the use of an optical sensor disposed adjacent to the radial bar code. Generally, operations involving the film spool and/or film cartridge, including for example, positioning the film spool to align a visual indicator or indicators, are referred to as "parking" the film spool. Typically, the film spool is parked after the film has been completely rewound into the film cartridge.
The door release of a camera typically opens a latch or otherwise allows a chamber door to open so that a film cartridge can be loaded or unloaded from the camera. Cameras can have several different operations, such as camera initialization, that occur after closing of the chamber door. After a thrust film cartridge has been loaded into a camera and the film door is closed, the camera needs to open the active light lock before film can be thrust from the film cartridge. When the user decides to rewind the film and eject the film cartridge, the camera must close the light lock door prior to opening the film door.
Locking mechanisms are known which prevent the opening a camera's film door when film is extended from a film cartridge. Many of these mechanisms lock or unlock the film door responsive to the presence or absence of a filmstrip in part of the film path of the camera. These mechanisms are practical for conventional film cartridges; but are risky for thrust cartridges, since the active light lock can be open even when all the film is wound into the canister. Thus, a user could possibly open the film door and extract the film cartridge before the film spool is parked, resulting in wasted film.
Various locking mechanisms are known for use with thrust film cartridges. Some mechanisms use the optical sensor and radial bar code for parking the film spool. These mechanisms have the shortcoming that in certain circumstances, the film spool may be improperly parked. This can result from many different factors, including optical sensor failure and/or misalignment of the radial bar code to the optical sensor. In the circumstance of an improperly parked film spool, a locking mechanism, which prevents the opening of a film door until the film spool is properly parked, would block the release of the film door and the photographic system user would be prevented from gaining access to the film cartridge.
It would thus be desirable to provide an active light lock coupled film door restraint and camera in which the spool of a thrust cartridge is mechanically parked and the film door is locked and unlocked mechanically, in coordination with spool parking.